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SEM images of lignin fiber: (a) overview image, (b) fused fibers, (c) voids at the fiber edge, (d) pores at the surface.
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Lightweight design is an essential part of the overall Volkswagen strategy for reducing the CO2 emissions. The use of carbon fiber offers an enormous lightweight potential. In comparison to steel enabling a mass reduction of up to 70% in automotive parts without a degradation of the functionalities is possible. Today, the use of carbon fiber is lim...
Citations
... FTIR analysis was employed to determine the chemical functionalities of KP at different temperatures, as shown in Fig. 4. Several significant peaks can be distinguished on liquefaction solvent, PEGGly in the range of 1000-1100 cm −1 (C-O-C stretching vibration), 2870 cm −1 (C-H stretching modes of aliphatic CH 3 , CH 2, and CH groups), and 3035-3670 cm −1 (O-H stretching band) [46]. The appearance of new peaks can be seen on KP samples at 1734 cm −1 (C=O stretch in hemicellulose or cellulose derivatives) [47,48], 1644 cm −1 (conjugated C=O groups due to the oxidation of lignin) [49], 1453 cm −1 (C-H in the aromatic ring) [50], 1350 cm −1 (O-H bending vibration) [51], 1215 cm −1 (C-O stretching vibration of phenolic and the presence of guaiacyl (G) ring) [52], 845 cm −1 (C=C and C-H bonds in the aromatic rings of biomass) [53] and 757 cm −1 (outof-plane aromatic deformation of lignin) [54]. When the temperature increases, the intensity peaks at 1644 cm −1 and 1734 cm −1 increased. ...
Production of kenaf polyols (KP) via liquefaction process was carried out using polyethylene glycol 400 and glycerol as the liquefying solvent. Optimization of parameters such as temperature, time, and the ratio of catalyst composition was done extensively. The effect of the hybridization of inorganic acid (sulphuric acid) and organic acid (lactic acid) as the liquefaction catalyst on the liquefaction product was studied. The results demonstrated that the lowest amount of residue (10.1%) was obtained at 160 °C with 3:1 (sulphuric acid: lactic acid) ratio of catalyst composition for 90 min. The hydroxyl (OH) number and viscosity of the kenaf polyol were examined. FTIR and NMR analyses revealed that most kenaf cellulose, hemicellulose, and lignin were degraded. XRD analysis was employed to examine the crystallinity index of kenaf residues (KR) at different temperatures, times, and catalyst ratio compositions. The morphology of KR at different temperatures was examined by using SEM analysis. The results showed that a smooth-surface KR was obtained at the optimum temperature (160 °C), indicating most of the cellulose was already decomposed at 160 °C. The optimized KP with OH number of 335.6 mg KOH/g and viscosity of 690 cP was used for the making of bio-based rigid polyurethane foam which is denoted as KPUF. The properties of KPUF and PUFs based petroleum polyol (PPUF) were compared. The density of KPUF (68.2 kg/m³) is lower compared to PPUF (131.9 kg/m³). The cellular structure and larger average cell diameter (0.617 mm) of KPUF enhance the water absorption ability which demonstrated that KPUF is capable to be utilized as growing media in the hydroponic system.
... During the last decades, lignin has been considered a promising raw material for producing low-cost CFs (Baker and Rials 2013;Gellerstedt et al. 2010), However, melt-spun lignin fibers has not exhibited sufficient mechanical properties and suffer from very long stabilization times in the CF production (Baker et al. 2012;Mainka et al. 2015). One approach to overcome these limitations is to blend lignin with a fiber forming polymer, preferably bio-based, such as cellulose. ...
... To prevent fusion, lignin must be heated slow enough to enable the chemical crosslinking to take place, which turns it into a thermoset. This has been a major challenge when producing CFs from melt spun lignin fibers, owing to the predominant use of melt-spinnable hardwood lignins with a low thermal reactivity (Baker et al. 2012;Mainka et al. 2015). Due to their higher glass transition temperature and more thermally reactive guaiacyl units, softwood lignins are easier to stabilize than hardwood lignins (Norberg et al. 2013). ...
Adhesion of fibers within a spun tow, including carbon fibers and precursors, is undesirable as it may interrupt the manufacturing process and entail inferior fiber properties. In this work, softwood kraft lignin was used together with a dissolving pulp to spin carbon fiber precursors. Lignin–cellulose precursors have previously been found to be prone to fiber fusion, both post-spinning and during carbon fiber conversion. In this study, the efficiency of applying different kinds of spin finishes, with respect to rendering separable precursors and carbon fibers, has been investigated. It was found that applying a cationic surfactant, and to a similar extent a nonionic surfactant, resulted in well separated lignin–cellulose precursor tows. Furthermore, the fiber separability after carbon fiber conversion was evaluated, and notably, precursors treated with a silicone-based spin finish generated the most well-separated carbon fibers. The underlying mechanism of fiber fusion post-spinning and converted carbon fibers is discussed.
Keywords: carbon fiber; lignin; surfactant
... In addition, the long stabilization time (over 100 h) [26] is problematic as well as the challenges in the melt spinning of kraft lignin without plasticizing additives [22,27]. The process of obtaining high-strength carbon fiber from the lignin is complex and needs careful control of melt spinning conditions, ramping profiles, and treatment temperatures. ...
Due to their outstanding material properties, carbon fibers are widely used in various industrial applications as functional or structural materials. This paper reviews the material properties and use of carbon fiber in various applications and industries and compares it with other existing fillers and reinforcing fibers. The review also examines the processing of carbon fibers and the main challenges in their fabrication. At present, two main precursors are primarily utilized to produce carbon fibers, i.e., polyacrylonitrile (PAN) and petroleum pitch. Each of these precursors makes carbon fibers with different properties. However, due to the costly and energy-intensive processes of carbon fiber production based on the existing precursors, there is an increasingly growing need to introduce cheaper precursors to compete with other fibers on the market. A special focus will be given to the most recent development of manufacturing more sustainable and cost-effective carbon fibers derived from petroleum asphaltenes. This review paper demonstrates that low-cost asphaltene-based carbon fibers can be a substitute for costly PAN/pitch-based carbon fibers at least for functional applications. The value proposition, performance/cost advantages, potential market, and market size as well as processing challenges and methods for overcoming these will be discussed.
... The melt spinning of different types of lignin to CF precursors have been investigated [5,[10][11][12][13][14][15]. Kraft lignin is available from kraft pulp mills and has a high carbon content (60-65 wt%). ...
... Kraft lignin is available from kraft pulp mills and has a high carbon content (60-65 wt%). Unfortunately, it is challenging to make CFs from melt-spun lignin precursors, as these precursors are brittle (hard to handle) and generally require a very long stabilization time (up to 100 h), making industrial production unfeasible [13]. The problem is that a melt-spinnable lignin is difficult to stabilize in a realistic period of time. ...
Citation: Bengtsson, A.; Landmér, A.; Norberg, L.; Yu, S.; Ek, M.; Brännvall, E.; Sedin, M. Carbon Fibers from Wet-Spun Cellulose-Lignin Precursors Using the Cold Alkali Process. Fibers 2022, 10, 108.
... The melt spinning of different types of lignin to CF precursors have been investigated [5,[10][11][12][13][14][15]. Kraft lignin is available from kraft pulp mills and has a high carbon content (60-65 wt%). ...
... Kraft lignin is available from kraft pulp mills and has a high carbon content (60-65 wt%). Unfortunately, it is challenging to make CFs from melt-spun lignin precursors, as these precursors are brittle (hard to handle) and generally require a very long stabilization time (up to 100 h), making industrial production unfeasible [13]. The problem is that a melt-spinnable lignin is difficult to stabilize in a realistic period of time. ...
In recent years, there has been extensive research into the development of cheaper and more sustainable carbon fiber (CF) precursors, and air-gap-spun cellulose-lignin precursors have gained considerable attention where ionic liquids have been used for the co-dissolution of cellulose and lignin. However, ionic liquids are expensive and difficult to recycle. In the present work, an aqueous solvent system, cold alkali, was used to prepare cellulose-lignin CF precursors by wet spinning solutions containing co-dissolved dissolving-grade kraft pulp and softwood kraft lignin. Precursors containing up to 30 wt% lignin were successfully spun using two different coagulation bath compositions, where one of them introduced a flame retardant into the precursor to increase the CF conversion yield. The precursors were converted to CFs via batchwise and continuous conversion. The precursor and conversion conditions had a significant effect on the conversion yield (12–44 wt%), the Young’s modulus (33–77 GPa), and the tensile strength (0.48–1.17 GPa), while the precursor morphology was preserved. Structural characterization of the precursors and CFs showed that a more oriented and crystalline precursor gave a more ordered CF structure with higher tensile properties. The continuous conversion trials highlighted the importance of tension control to increase the mechanical properties of the CFs.
... The structural changes of lignin during melt blowing were investigated, including spinning and pelletizing, finding that the signals for the phenylcoumaran B 2 ′ ,6 ′ as well as S 2 ′ ,6 were not detectable anymore, and new signals for olefinic bonding, were detected with possible reactions shown in Fig. 6a,b. Further reactions are the formation of carboxylic acids or ketone, Fig. 6c [107]. ...
... The reaction of lignin during melt blowing and the morphology of lignin-based carbon fibers: (a) oxidation reaction; (b) lignin olefinic bonding during melt blowing; (c) formation of carboxylic acid or ketone; (d) overview and partially enlarged SEM images of lignin fibers (reorganized and modified from[107]). ...
Lignin remains the second abundant source of renewable carbon with an aromatic structure. However, most of the lignin is burnt directly for power generation, with an effective utilization rate of <2 %, making value addition on lignin an urgent requirement. From this perspective, preparation of lignin-based carbon fibers has been widely studied as an effective way to increase value addition on lignin. However, lignin species are diverse and complex in structure, and the pathway that enables changes in lignin structure during pretreatment, fiber formation, stabilization, and carbonization is still uncertain. In this review, we condense the common structural evolution route from the previous studies, which can serve as a guide towards engineered lignin carbon fibers with high performance properties.
... The proton 90 • pulse was set to 2.55 μs and the decoupling strength during acquisition was 54 kHz. The samples were pulverized and mixed with an equal weight of hydrated magnesium silicate to reduce large current generation under RF excitation [32]. The pyrolysis products of HKL, HN and SHN were characterized using a pyrolysis gas chromatography-mass spectrometer (GCMS-QP 2010, Shimadzu, Japan) at 600 • C. ...
... The peak at 3030 cm − 1 and 2927 cm − 1 corresponds to the stretching vibration of the aromatic group C-H and the stretching vibration of the aliphatic group C -H, respectively [42,43]. The degree of aromatization is usually expressed as the ratio of the peak integral areas at 3030 cm − 1 and 2927 cm − 1 [32]. On this basis, the aromatization degrees of SHNs prepared at different pre-oxidation temperatures were calculated and showed that the SHNs pre-oxidized at 280 • C had the highest aromatization degree (Table S7). ...
Lignin is a biopolymer with high carbon content, making lignin-based carbon fiber an important research direction. In the process of carbonization to prepare carbon fibers, lignin fibers are easily softened and fused, which destroys the microstructure of fibers, thereby reducing the quality of lignin-based carbon fibers. Therefore, it is non-negligible to pre-oxidize lignin fibers before carbonization to prevent fiber fusion and maintain fiber structure. Therefore, the effects of pre-oxidation temperature and heating rate on the structure of pre-oxidation lignin fibers with controllable diameter and thickness prepared by melt-blowing were studied in detail. During pre-oxidation, crosslinking and aromatization of lignin fibers occurred, and alkyl and benzene rings were mainly oxidized to form carbonyl groups. The aromatization degree of the pre-oxidized product was recorded at 280 °C and 0.25 °C/min, and the oxygen content reached 15 %–20 %, making it suitable for the preparation of bio-based carbon fibers. On this basis, carbon fibers with porous morphology can be prepared with a graphitization of 0.54 and a resistivity of 0.02 Ω cm⁻¹. These materials are expected to be applicable in sensors, catalytic materials and other fields.
... 4−7 The most favorable characteristics of kraft lignin are its high carbon content (60−65 wt %) and availability, but CFs made from melt-spun lignin PFs generally require very long stabilization times, sometimes over 100 h, making industrial production not feasible. 8,9 Furthermore, for a successful melt spinning of lignin, the thermal properties of lignin are very important, and pretreatments such as solvent extraction and membrane filtration of the lignin is often necessary. To overcome this challenge, lignin has been derivatized and/or coprocessed with other polymers. ...
... 19 The different CF morphology obtained in the present work is attributed to the use of softwood lignin instead of hardwood lignin, as the former has a higher thermal reactivity, which results in the formation of less volatiles that may result in detrimental voids during conversion. 8,9,23 The CFs in the present work were partially separable by hand. Some fiber−fiber joints in the PF tow were observed ( Figure S3), and these were preserved after conversion into CF, suggesting that a different spin finish and/or application is necessary. ...
The demand for carbon fibers (CFs) based on renewable raw materials as the reinforcing fiber in composites for lightweight applications is growing. Lignin-cellulose precursor fibers (PFs) are a promising alternative, but so far, there is limited knowledge of how to continuously convert these PFs under industrial-like conditions into CFs. Continuous conversion is vital for the industrial production of CFs. In this work, we have compared the continuous conversion of lignin-cellulose PFs (50 wt % softwood kraft lignin and 50 wt % dissolving-grade kraft pulp) with batchwise conversion. The PFs were successfully stabilized and carbonized continuously over a total time of 1.0-1.5 h, comparable to the industrial production of CFs from polyacrylonitrile. CFs derived continuously at 1000 °C with a relative stretch of -10% (fiber contraction) had a conversion yield of 29 wt %, a diameter of 12-15 μm, a Young's modulus of 46-51 GPa, and a tensile strength of 710-920 MPa. In comparison, CFs obtained at 1000 °C via batchwise conversion (12-15 μm diameter) with a relative stretch of 0% and a conversion time of 7 h (due to the low heating and cooling rates) had a higher conversion yield of 34 wt %, a higher Young's modulus (63-67 GPa) but a similar tensile strength (800-920 MPa). This suggests that the Young's modulus can be improved by the optimization of the fiber tension, residence time, and temperature profile during continuous conversion, while a higher tensile strength can be achieved by reducing the fiber diameter as it minimizes the risk of critical defects.
... hydroxyl groups in lignin [86]. ...
... Comparison TGA curve of LNP isolated from Eucalyptus and mild wood. Adapted from Zhang et al.[86]. ...
Each year, 50 to 70 million tonnes of lignin are produced worldwide as by-products from pulp industries and biorefineries through numerous processes. Nevertheless, about 98% of lignin is directly burnt to produce steam to generate energy for the pulp mills and only a handful of isolated lignin is used as a raw material for the chemical conversion and for the preparation of various substances as well as modification of lignin into nanomaterials. Thus, thanks to its complex structure, the conversion of lignin to nanolignin, attracting growing attention and generating considerable interest in the scientific community. The objective of this review is to provide a complete understanding and knowledge of the synthesis methods and functionalization of various lignin nanoparticles (LNP). The characterization of LNP such as structural, thermal, molecular weight properties together with macromolecule and quantification assessments are also reviewed. In particular, emerging applications in different areas such as UV barriers, antimicrobials, drug administration, agriculture, anticorrosives, the environment, wood protection, enzymatic immobilization and others were highlighted. In addition, future perspectives and challenges related to the development of LNP are discussed.
... The price of precursor fibre (PF) accounts for almost half of the entire cost of CF manufacture [97]. The petroleum-derived polymer polyacrylonitrile (PAN), which contributes for 50% of the price of carbon fibre, is one of the most often used precursors today [98]. To save costs, researchers have looked at using cheaper alternatives like lignin as carbon fibre precursors. ...
The pulp and biorefining industries produce their waste as lignin, which is one of the most abundant renewable resources. So far, lignin has been remained severely underutilized and generally burnt in a boiler as a low-value fuel. To demonstrate lignin's potential as a value-added product, we will review market opportunities for lignin related applications by utilizing the thermo-chemical/biological depolymerization strategies (with or without catalysts) and their comparative evaluation. The application of lignin and its derived aromatics in various sectors such as cement industry, bitumen modifier, energy materials, agriculture, nanocomposite, biomedical, H2 source, biosensor and bioimaging have been summarized. This comprehensive review article also highlights the technical, economic, environmental, and socio-economic variable that affect the market value of lignin-derived by-products. The review shows the importance of lignin, and its derived products are a platform for future bioeconomy and sustainability.
